Permanent magnet motor or actuator with field weakening capability

ABSTRACT

The present disclosure relates generally to a permanent magnet, brushless motor comprising a primary rotor having alternating magnetic poles around a circumference, a secondary rotor similar to the primary rotor. The primary rotor may be free to rotate by approximately plus or minus one pole of the secondary rotor. As such, when the two rotor components have opposite polarities aligned, the motor may be in a field weakened state. Generally, the field weakened state may be the normal state of the motor. As a significant load is encountered, the rotors may automatically transition to a non-weakened state wherein similar polarities are aligned on the rotors. A permanent magnet, brushless motor as described herein may be employed at a motor level or integrated into a linear actuator, wherein the rotor of the permanent magnet, brushless motor may include a hollow shaft.

FIELD OF THE INVENTION

The present disclosure relates to apparatus and methods for a servoactuator or motor. More particularly, the present disclosure relates toapparatus and methods for a servo actuator or permanent magnet,brushless motor having field weakening capability.

BACKGROUND OF THE INVENTION

Various industries, and particularly the manufacturing industry, amongothers, have utilized rotary motors and linear actuators to controlmovements of automated welding guns, automated clamping fixtures, andthe like. For example, in the automotive industry, injection moldingindustry, and various other industries, actuation and control of weldingguns and clamping fixtures and controlled linear movement of otherfixtures and devices have been accomplished using fluid actuators, suchas pneumatic or hydraulic actuators. While fluid actuators havefunctioned reasonably well for these purposes, they inherently embodyvarious limitations. One, because of the possibility of leaks andfailure of seals, etc., there is always the concern of contamination ofthe worksite by a leaking fluid. Second, fluid actuators necessarilyrequire a source of pressurized fluid, and thus, a fluid supply system.This leads to significant maintenance and other costs. Third,limitations sometimes exist with respect to the accuracy and positioningof linear movement and the adjustability of such movement.

The use of permanent magnet, brushless motors is also well known. Apermanent magnet, brushless motor is described in co-pending U.S. patentapplication Ser. No. 11/031,539, filed Jan. 7, 2005, entitled “ElectricActuator,” and published as Publication No. 2005/0253469, the entiretyof which is hereby incorporated by reference herein. The relationshipbetween the rotation and torque of prior art permanent magnet, brushlessmotors is inversely proportional. That is, as the torque linearlydecreases, the rotation speed, or number of rotations, increases.

In some prior art permanent magnet, brushless motors, a field weakeningtechnique wherein the total magnetic flux is lowered to achieve highspeed rotation has been employed. For example, a brushless motor thatincludes a field weakening technique is described in U.S. Pat. No.5,821,710, issued to Masuzawa, et al. The brushless motor in Masuzawaincludes two field permanent magnets having poles of differentpolarities alternately arranged in the direction of rotation, whereinone of the field permanent magnets is rotatable with respect to theother field permanent magnet. A mechanism for changing the phase of themagnetic poles of the field permanent magnets is provided to place thefield permanent magnets out of phase as rotation increases. Themechanism uses arc-shaped governors held in a default, low rotationposition using springs. The governors are forced into a high rotationposition due to centrifugal force caused by the higher speed rotation.The high rotation position causes the field permanent magnets to bepositioned out of phase, thus weakening the magnetic field.

Accordingly, there is a need in the art for improved apparatus andmethods for a permanent magnet, brushless motor having field weakeningcapability which overcomes the deficiencies and limitations of the priorart. Particularly, there is a need in the art for apparatus and methodsfor a permanent magnet, brushless motor that may automaticallytransition from a field weakened position upon encountering asignificant load.

BRIEF SUMMARY OF THE INVENTION

The present invention, in one embodiment, is a permanent magnet,brushless motor including first and second rotors having magnets spacedcircumferentially around the outer surfaces thereof. Upon receiving aload, the rotors are automatically rotated relative to one another froma first position to a second position. In the first position, thepolarity of the magnets on the first rotor is aligned with magnets ofopposite polarity on the second rotor. In the second position, thepolarity of the magnets on the first rotor is aligned with magnets ofsimilar polarity on the second rotor. The relative configuration of thefirst and second rotors can be controlled by any of several meansdisclosed here.

The present invention, in another embodiment, is a method of increasingtorque including rotating a motor, applying a load to the motor, andoperably decoupling first and second rotors of the motor, such that therotors are rotationally shifted with respect to each other into anincreased torque position. The method may further comprise reducing theload such that the rotors are rotationally shifted with respect to eachother back into the initial position.

The present invention, in yet another embodiment, is a motor includingfirst and second rotors having magnets spaced circumferentially aroundthe outer surfaces thereof and means for operably decoupling the firstrotor from the second rotor. The rotors are decoupled from a default,low torque position into a high torque position based on reaching athreshold, increased load received by the motor.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. As will be realized, theinvention is capable of modifications in various obvious aspects, allwithout departing from the spirit and scope of the present invention.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter that is regarded as formingthe various embodiments of the present invention, it is believed thatthe invention will be better understood from the following descriptiontaken in conjunction with the accompanying FIGURES, in which:

FIG. 1 is a side cross-section of one embodiment of a permanent magnet,brushless motor in accordance with the present disclosure.

FIG. 2 is an isometric view of the primary and secondary rotors and therotor configuration mechanism of the permanent magnet, brushless motorof FIG. 1 in accordance with the present disclosure.

FIG. 3 is a plan view of an alternate embodiment of the rotorconfiguration mechanism.

FIG. 4 is a side cross-section of an alternate embodiment of thepermanent magnet, brushless motor of FIG. 1.

The present disclosure includes novel and advantageous apparatus andmethods for a permanent magnet, brushless motor with field weakeningcapability. More particularly, the present disclosure relates toapparatus and methods for a permanent magnet, brushless motor that maytransition automatically between a weakened state and a non-weakenedstate. More particularly, the present disclosure relates to apparatusand methods for a permanent magnet, brushless motor that may transitionautomatically from a weakened state to a non-weakened state uponencountering a significant load. A weakened state may allow for higherrotation speeds achieved by reducing the back electromotive force(“BEMF”) or generator properties of the motor. The permanent magnet,brushless motor with field weakening capability may be used for purelyrotary applications as well as included in an actuator. Similarly, thepermanent magnet, brushless motor with field weakening capability may betuned or adapted to the particular application of use.

Generally, a secondary rotor component having alternating magnetic polesaround a circumference may be provided. A primary rotor component mayfurther be provided, wherein the primary rotor component is similar tothe secondary rotor component and rotates at the same speed as thesecondary rotor component. However, the primary rotor component may befree to rotate by approximately plus or minus (“+/−”) one pole of thesecondary rotor component. As such, when the two rotor components haveopposite polarities aligned, or are out of phase with each other, themotor may be in a field weakened state. Generally, the field weakenedstate may be the normal, or default, state of the motor. As asignificant load is encountered, the rotor components may automaticallytransition to a non-weakened state wherein similar polarities arealigned on the rotor components. A permanent magnet, brushless motor asdescribed herein may be employed at a motor level or integrated into alinear actuator, wherein the rotor of the permanent magnet, brushlessmotor may include a hollow shaft such that a screw may be run throughthe center of the motor. Some applications in which a permanent magnet,brushless motor may be used in purely rotary applications include, butare not limited to, a vacuum pump or hybrid vehicle. Similarly, apermanent magnet, brushless motor may be used in an actuator to controlmovements of automated robotic, pedestal, or fixture welding guns,automated clamping fixtures, etc.

In describing motor embodiments of the present disclosure, the terms“proximal” and “distal” will sometimes be used to definedirections/orientations relative to the motor. Specifically, the term“proximal” shall mean the direction which is toward an end of the motorthat is opposite a load receiving end, while the term “distal” shallmean the direction which is toward the connection end, or load receivingend, of the motor.

In one embodiment, a permanent magnet, brushless motor 100, asillustrated in FIG. 1, may include a motor housing comprising of aproximal head end or block 10, a distal head end or block 12, and acentrally positioned peripheral housing portion 14. As shown, thehousing portion 14 may be positioned between the end blocks 10 and 12and may be retained in that position between the blocks 10 and 12 in aconventional or other suitable manner. A motor 100 may generallycomprise a plurality of motor windings 16, a plurality of motor magnets18, a primary rotor 22, and a secondary rotor 20 positioned between theend blocks 10 and 12 and radially inwardly of the housing portion 14.

As was previously mentioned, the motor 100 may be used as a linearactuator. For example, a threaded, elongated shaft or lead screw andother suitable components may be included in the motor 100, positionedradially inwardly from the secondary 20 and primary 22 rotors andfunction to convert rotational motion of the rotors 20, 22 to linearmovement of the lead screw or other suitable load transfer member, suchas a threaded nut circumferentially surrounding the lead screw. As usedherein, the term “thread” or “threaded” may include any conventional orother threads such as ACME threads, roller screw threads, ball nutthreads, or any means known in the art to convert rotational motion tolinear motion.

With reference to FIGS. 1 and 2, the motor 100 may comprise a primaryrotor 22, a secondary rotor 20, and one or more stationary motorwindings 16. The windings 16 may be positioned radially outwardly of therotors 20, 22 and fixed relative to the motor housing 14. The rotors 20,22 may be generally cylindrical members having generally cylindricalouter surfaces. Alternatively, the windings 16 may be positionedradially inwardly of the rotors 20, 22 in a fixed position as suggestedby the motor arrangement shown in FIG. 4.

The secondary rotor 20 may be provided with a plurality of motor magnets18. As shown, the magnets 18 may be mounted so that they extend axiallyalong an outer surface of the secondary rotor 20 between its proximaland distal ends. In the embodiment of FIG. 2, the magnets 18 may beattached to the outer surface of the secondary rotor 20 and may protruderadially from the outer surface. In other embodiments, the magnets 18may be inlaid within an outer surface portion of the secondary rotor 20.For example, axially extending portions of the outer surface of thesecondary rotor 20 may be removed by machining or the like to formaxially extending channels or grooves around the cylindrical peripheryof the secondary rotor 20. These channels or grooves may permit themagnets 18 to be inlaid within these channels or grooves in the outersurface of the secondary rotor 20. In yet further embodiments, themagnets 18 may be inlaid or embedded within the rotor such that noportion of the magnet protrudes from the outer surface of the secondaryrotor 20, and in some cases, may be completely embedded within thesecondary rotor 20, such that no portion of the magnets 18 is on theouter surface of the secondary rotor 20.

The axially extending magnets 18 may be separated circumferentiallyaround the secondary rotor 20, as can be seen in FIG. 2. Additionally,the magnets 18 may alternate in polarity circumferentially around thesecondary rotor 20. That is, if an axially extending magnet 18 has aNorth polarity, then the next circumferentially located magnet 18 mayhave a South polarity, and so on.

The secondary rotor 20 may extend axially within the primary rotor 22,described in further detail below. The secondary rotor 20 may further beoperably connected to a load or load receiving end of the motor 100. Thesecondary rotor 20 and the primary rotor 22 may be rotatable relative toeach other. As such, the primary 22 and secondary 20 rotors, at sometimes, may be aligned such that the polarity of the magnets 18 providedon the secondary rotor 20 are aligned, or in phase, with the magnets 18of similar polarity provided on the primary rotor 22. At other times,the polarity of the magnets 18 provided on the secondary rotor 20 is notaligned with the magnets 18 of similar polarity provided on the primaryrotor 22. And, at yet other times, the polarity of the magnets 18provided on the secondary rotor 20 are aligned with the magnets 18 ofopposite polarity provided on the primary rotor 22.

A stop 24, extending radially outward from the secondary rotor 20, maybe operably connected to a proximal end of secondary rotor 20. Infurther embodiments, more than one stop 24 may be operably connected toa proximal end of the secondary rotor 20. A magnet 25 comprising a firstportion of a magnetic coupling device 26 may also be operably connectedto a proximal end of the secondary rotor 20. In one embodiment, themagnet 25 comprising the first portion of the magnetic coupling device26 may be located on an outer surface of the portion of the secondaryrotor 20 extending radially within the primary rotor 22. In a furtherembodiment, the magnet 25 comprising the first portion of the magneticcoupling device 26 may comprise six poles of one inch, 30 degreemagnets. Another portion of the magnetic coupling device 26 may beoperably coupled to a proximal end of the primary rotor 22, as will bediscussed in further detail. It is recognized, however, that themagnetic coupling device 26 may be located at any suitable locationaxially along the primary 22 and secondary 20 rotors. The magneticcoupling device 26 may operably couple the primary 22 and secondary 20rotors in a default, high speed rotation configuration. That is, themagnetic coupling device 26 may operably couple the secondary 20 andprimary 22 rotors in a default position, wherein the polarity of themagnets 18 provided on the secondary rotor 20 are aligned with themagnets 18 of opposite polarity provided on the primary rotor 22.

It is noted that other suitable coupling devices may be used to achievethe same effect in accordance with the present invention. For example,high durometer resilient elastomeric biasing springs 40 can be providedas shown in FIG. 3. These springs 40 provide a different torque responsecharacteristic to the motor than the torque response provided by themagnetic coupling devices 26 described above.

The primary rotor 22 may be described in a substantially similar manneras the secondary rotor 20. That is, the primary rotor 22 may be providedwith a plurality of motor magnets 18. As shown, the magnets 18 may bemounted so that they extend axially along an outer surface of theprimary rotor 22 between its proximal and distal ends. In oneembodiment, the magnets 18 may be attached to the outer surface of theprimary rotor 22 and may protrude radially from the outer surface. Inother embodiments, the magnets 18 may be inlaid within an outer surfaceportion of the primary rotor 22. For example, axially extending portionsof the outer surface of the primary rotor 22 may be removed by machiningor the like to form axially extending channels or grooves around thecylindrical periphery of the primary rotor 22. These channels or groovesmay permit the magnets 18 to be inlaid within these channels or groovesin the outer surface of the primary rotor 22. In yet furtherembodiments, the magnets 18 may be inlaid or embedded within the rotorsuch that no portion of the magnet protrudes from the outer surface ofthe primary rotor 22, and in some cases, may be completely embeddedwithin the primary rotor 22, such that no portion of the magnets 18 ison the outer surface of the primary rotor 22.

The axially extending magnets 18 may be separated circumferentiallyaround the primary rotor 22, as can be seen in FIG. 2. Additionally, themagnets 18 may alternate in polarity circumferentially around theprimary rotor 22. That is, if an axially extending magnet 18 has a Northpolarity, then the next circumferentially located magnet 18 may have aSouth polarity, and so on.

The primary rotor 22 may be operably coupled to a rotary encoder orother similar means. The rotary encoder may be used to phase the motor100 to the primary rotor 22. That is, the position of the primary rotor22 in relation to the windings 16 may define the phasing of the motor100. By establishing a reference of the primary rotor 22 to an encoderindex pulse or absolute encoder position, a drive for the motor 100 canknow how to commutate.

The primary rotor 22 may further include one or more blocks 28 alignedwith the stop(s) 24 operably coupled to the secondary rotor 20. A block28 of the primary rotor 22 may engage with a stop 24 of the secondaryrotor 20 to retain the primary rotor 22 from over-rotation. That is, ablock 28 may engage with a stop 24 to keep the primary rotor 22 fromrotating more than +/− one pole of the magnets 18 of the secondary rotor20. Generally, a block 28 of the primary rotor 22 may only engage a stop24 of the secondary rotor 20 while the primary 22 and secondary 20rotors are not operably connected by the magnetic coupling device 26, orother suitable coupling device.

A magnet comprising a second portion of the magnetic coupling device 26may be operably connected to the primary rotor 20. In one embodiment,the magnet comprising the second portion of the magnetic coupling device26 may be located on an inner surface of the primary rotor 20, whichextends radially around the secondary rotor 22. In a further embodiment,the magnet comprising the second portion of the magnetic coupling device26 may comprise six poles of one inch, 30 degree magnets. As previouslydescribed, the magnetic coupling device 26 may function to operablyretain the secondary 20 and primary 22 rotors in a default, high speedrotation configuration.

The motor 100 may be used for linear or rotary applications. In a linearembodiment, for example, a threaded, elongated shaft or lead screw 30and other suitable components may be included in the motor 100,positioned radially inwardly from the secondary 20 and primary 22 rotorsand function to convert rotational motion of the rotors 20, 22 to linearmovement of the lead screw 30 or other suitable load transfer member,such as a threaded nut 34 circumferentially surrounding the lead screw30. In an alternative embodiment, the lead screw 30 may be linearlyattached at or near the distal end of the secondary rotor 20, such thatthe lead screw 30 is positioned in-line with the secondary rotor 20rather than positioned radially inwardly from the secondary 20 andprimary 22 rotors. Such may be the case when the lead screw 30 has toolarge a diameter for efficiently positioning radially inwardly from thesecondary 20 and primary 22 rotors. In one embodiment, the lead screw 30may have about a two inch outer diameter. In other embodiments, the leadscrew 30 may have other outer diameters, such as but not limited to,about 1 inch, 1½ inch, 1¾ inch, or 2¼ inch.

In one embodiment, the housing portion 14 may comprise a first andsecond housing portion. Each housing portion may comprise aself-contained unit, the first housing portion having the secondary 20and primary 22 rotors and the second housing portion having the leadscrew 30 and other actuator components. The two self-contained units maybe manufactured independently and integrated together. In oneembodiment, the two self-contained units may be integrated together withtie rods. In a further embodiment, a coupling unit 36 may be positionedbetween the self-contained units. In one embodiment, the coupling unit36 may be manufactured of reinforced neoprene with a steel body. Thecoupling unit 36, in yet a further embodiment, may have a peak torquerating of about 4,700 in-lbs to 250° F.

The motor 100 may further comprise a thrust assembly comprising at leasta thrust tube 32 and a threaded nut 34. The thrust tube 32 may beoperably coupled to the threaded nut 34 and move linearly in conjunctiontherewith along the lead screw 30. As the lead screw 30 rotates, thethreaded nut 34 may be held from rotation, thereby causing the threadednut 34, and therefore, the thrust assembly, to move linearly along thelead screw 30. As used herein, the term “thread” or “threaded” mayinclude any conventional or other threads such as ACME threads, rollerscrew threads, ball nut threads, or any means known in the art toconvert rotational motion to linear motion.

In some embodiments, an anti-rotation rod 38 may be provided to guidethe rotational orientation of the thrust tube 32. In other words, theanti-rotation rod 38 may retain the thrust tube 32 from rotating. Theanti-rotation rod 38 may be removable, for example, where the motor 100is used with guided tooling and an anti-rotation rod 38 is not desired.The anti-rotation rod 38 may be removably attached to a portion of thethrust tube 32, the threaded nut 34, or any other component that is partof the thrust assembly.

In further embodiments, the motor 100 may include an integrated warningfor maintenance/failure of the motor 100. In one embodiment, theintegrated warning may indicate that the motor 100 has failed orrequires maintenance. In other embodiments, the integrated warning mayindicate that the motor 100 is about to fail or should have a checkup.In some embodiments, the integrated warning may signify that the motor100 has reached its estimated useful life or is about to reach itsestimated useful life.

Specifications, requirements, and sizes of a motor 100 in accordancewith the present disclosure may be varied and configured for a varietyof applications. In one embodiment, the motor 100 may have a force ofgenerally between 8,000 and 25,000 pounds. However, in otherembodiments, the motor 100 may have a lesser or greater forcecharacteristic. The motor 100 may have a maximum speed of about 20inches per second. However, in alternative embodiments the maximum speedmay be slower or faster than 20 inches per second. The motor may bedesigned for different voltage requirements, e.g., 400 Vac, 460 Vac, 575Vac, etc. Furthermore, the motor 100 may be configured for differentstroke lengths, such as 6 inch, 12 inch, or shorter or longer strokelengths.

Having described the structure of the embodiment of FIGS. 1 and 2, itsoperation can be described as follows. The motor 100 may be driven by DCor AC current. In one embodiment, the motor 100 may typically be drivenby sinusoidal or AC current. When the motor 100 is actuated, thesecondary 20 and primary 22 rotors may be caused to rotate in a firstdirection. That is, the windings 16 may cause the secondary 20 andprimary 22 rotors to rotate. The secondary 20 and primary 22 rotors mayrotate in the same direction. Furthermore, where the load is notsignificant enough to cause the magnetic coupling device 26 to uncouple,the primary 22 and secondary 20 rotors may be operably coupled such thatthey may rotate at the same rotational speed and are aligned in adefault position, wherein the polarity of the magnets 18 provided on thesecondary rotor 20 are aligned with the magnets 18 of opposite polarityprovided on the primary rotor 22. The default position, as illustratedin FIG. 2, may be used generally for high speed rotation in which lesstorque is required.

When a significant load is encountered by the motor 100, the magneticcoupling device 26 may become uncoupled. Specifically, in oneembodiment, the magnetic coupling device 26 may slowly collapse theweakened field as the load increases. Therefore, the primary rotor 22may be automatically caused to rotate relative to the secondary rotor20, such that a stop 24 of the secondary rotor 20 engages a block 28 ofthe primary rotor 22. When the secondary 20 and primary 22 rotors are inthis second, low speed position, the polarity of the magnets 18 providedon the secondary rotor 20 are aligned with the magnets 18 of similarpolarity provided on the primary rotor 22, thereby increasing the torqueprovided by the motor 100. In some embodiments, the primary rotor 22 maybe automatically rotated relative to the secondary rotor 20, such thatthe primary rotor 22 and secondary rotor 20 are in a position betweenthe default position and the second, low speed position. In furtherembodiments yet, the primary rotor 22 may be automatically and graduallyrotated relative to the secondary rotor 20 from the default position tothe second, low speed position, and vice versa, as the load graduallyincreases or decreases, respectively. As the primary rotor 22 andsecondary rotor 20 rotate relative to each other towards the second, lowspeed position, the torque of the motor 100 may increase. When the loadencountered decreases or is caused to decrease, the magnetic couplingdevice 26 may cause the secondary 20 and primary 22 rotors to becomeoperably recoupled in the default, high speed position, wherein thepolarity of the magnets 18 provided on the secondary rotor 20 arealigned with the magnets 18 of opposite polarity provided on the primaryrotor 22. The load at which the magnetic coupling device 26 becomesuncoupled may be varied, for example but not limited to, by varying thesize of the magnetic coupling device 26. In one embodiment, the magneticcoupling device may be configured for a quick collapse above about 800lbs. of force.

It will be understood that the biasing spring coupler/decoupler of FIG.3 can be substituted for that of the magnetic coupling device 26 withoutdeparting from the scope of the invention.

In one embodiment, the primary rotor 22 may have a greater number ofmagnets than the secondary rotor 20. The windings 16 may be initiallyphased to the primary rotor 22. The magnetic coupling device 26 may holdthe poles of the magnets 18 on the primary rotor 22 misaligned with thepoles of the magnets 18 on the secondary rotor 20. As the loadincreases, and current is increased to the windings 16, the magneticcoupling device 26 is eventually overcome and the poles of the magnets18 on the primary 22 and secondary 20 rotors align. In this position,both the primary 22 and secondary 20 rotors are transmitting torque tothe load.

Furthermore, the primary 22 and secondary 20 rotors may be caused torotate together in an opposite or second direction, thereby reversingthe motor 100. In such second direction, operation of the primary 22 andsecondary 20 rotors may generally be the same as described in relationto the first direction.

Although the present invention has been described with reference topreferred embodiments, persons skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. For example, components other than use of amagnetic coupling device may be used for coupling the secondary andprimary rotors. Similarly, components other than a stop and block may beused to retain the primary rotor from over-rotation.

1. A permanent magnet, brushless motor comprising: a housing having aproximal end, a distal end, and a longitudinal axis extending betweenthe proximal and distal ends; a fixed motor winding located inside thehousing and coaxially aligned with the longitudinal axis of the housing;first and second rotors located inside the housing and coaxially alignedwith the longitudinal axis and being rotationally moveable relative tothe housing, to the motor winding, and to each other, the first rotorand second rotor each having spaced magnets mounted on surfaces thereof;a coupling device located between the first rotor and the second rotorthat operably couple the first rotor and the second rotor in a firstposition; wherein upon encountering a load, the first rotor ismechanically rotated relative to the second rotor from a first positionto a second position whereby higher torque is generated; wherein in thefirst position, the polarity of the magnets provided on the first rotorare aligned with the magnets of opposite polarity provided on the secondrotor; and wherein in the second position, the polarity of the magnetsprovided on the first rotor are aligned with the magnets of similarpolarity provided on the second rotor.
 2. The permanent magnet,brushless motor of claim 1, wherein the second rotor comprises a stoptab extending radially outward from the second rotor.
 3. The permanentmagnet, brushless motor of claim 2, wherein the first rotor comprises ablock for engaging the stop tab of the second rotor when the first rotoris in the second position.
 4. The permanent magnet, brushless motor ofclaim 1, wherein the first position is a default low torque position. 5.The permanent magnet, brushless motor of claim 3, wherein upon reductionof the load, the first rotor is mechanically rotated relative to thesecond rotor from the second position to the first position.
 6. Thepermanent magnet, brushless motor of claim 1, wherein the couplingdevice is a magnetic coupling device.
 7. The permanent magnet, brushlessmotor of claim 1 wherein the coupling device includes biasing means. 8.The permanent magnet, brushless motor of claim 1, wherein upon reductionof the load, the first rotor is mechanically rotated relative to thesecond rotor from the second position to the first position.
 9. Thepermanent magnet, brushless motor of claim 1, further comprising meansof linear actuation.
 10. A method of increasing torque comprising:rotating a motor comprising a fixed motor winding and a first and secondrotor coaxially aligned inside a housing, the first rotor and secondrotor being rotationally moveable relative to the housing, to the motorwinding and to each other, first rotor and second rotor each includecircumferentially spaced magnets located thereon, wherein the first andsecond rotors are in an initial position and in a field weakened statefor increased rotational speed; applying a load to the motor; andoperably decoupling the first and second rotors relative to each other,such that the first and second rotors are rotationally shifted withrespect to each other into a field non weakened state with an increasedtorque position.
 11. The method of claim 10, wherein in the initialposition, the magnets provided on the first rotor are aligned withmagnets of opposite polarity on the second rotor, and in the increasedtorque position, the magnets provided on the first rotor are alignedwith magnets of similar polarity on the second rotor.
 12. The method ofclaim 11, wherein decoupling the first and second rotors relative toeach other comprises reconfiguring a coupling device which operablycouples the first and second rotors upon reaching a threshold load. 13.The method of claim 12, further comprising reducing the load such thatthe first and second rotors are rotationally shifted with respect toeach other back to the initial position, and the coupling means operablyrealigns the first and second rotor.
 14. The method of claim 10, furthercomprising reducing the load such that the first and second rotors arerotationally shifted with respect to each other back to the initialposition.
 15. A motor comprising: a housing; a fixed motor windinglocated inside the housing; first and second rotors coaxially alignedand located inside the housing and being rotationally moveable relativeto the housing to the motor winding, and to each other, the first andsecond rotors having circumferentially spaced magnets on outer surfacesthereof; and means utilizing torque created within the motor foroperably decoupling the first rotor from the second rotor from adefault, low torque position to a high torque position based on reachinga threshold, increased load received by the motor.
 16. The motor ofclaim 15, further comprising means for operably realigning the firstrotor with the second rotor in the default, low torque position based ona reduction of load received by the motor.
 17. The motor of claim 16,wherein the motor is a permanent magnet, brushless motor.
 18. The motorof claim 16, wherein the second rotor includes a tab.
 19. The motor ofclaim 18, wherein the first rotor comprises a block for engaging the tabof the second rotor when the first and second rotors are in the hightorque position, whereby the first and second rotors are retained fromover rotation with respect to each other.